While semiconductor components are used in various systems such as an optical system and a drive system, it is known that characteristics of these semiconductor components change depending on the temperature. Thus, in order to measure the temperature and correct changes of the characteristics, temperature sensors are mounted. While these temperature sensors are required to have high detection efficiency, these temperature sensors are also required to be small and inexpensive, for example.
FIGS. 7A and 7B are block diagrams of temperature detection circuits disclosed in Patent Document 1 as conventional techniques. In FIGS. 7A and 7B, a constant current is caused to flow through a pn junction diode, and by using change of the temperature-dependent forward on-voltage, the temperature is measured.
FIG. 7C illustrates a configuration of a temperature detection circuit disclosed in Patent Document 1 as an invention. While a threshold voltage Vth and a drain current Ids are temperature-dependent parameters of a metal-oxide semiconductor (MOS) transistor, this document discloses a technique that aims to eliminate an impact of the temperature dependence of the threshold voltage Vth and to measure the temperature by using only the temperature characteristics of the drain current Ids. Specifically, the temperature detection circuit of FIG. 7C includes a potential control circuit 10 connected to a gate of a MOS transistor M0, to cancel out the temperature dependence of the threshold voltage Vth. Assuming that a threshold voltage and a gate voltage of the MOS transistor M0 are designated by Vth and Vgs, respectively, the potential control circuit 10 supplies a voltage to the gate of the MOS transistor M0, so that Vgs-Vth remains at a constant level regardless of the temperature.
FIG. 8A is a block diagram illustrating an overall configuration of a conventional temperature detection circuit disclosed in Patent Document 2, and FIGS. 8B and 8C are circuit diagrams of first and second voltage source circuits in FIG. 8A, respectively. According to Patent Document 2, by changing work functions (Vth) of field-effect transistors M1 and M2, an output voltage VPN, which is a gate-source voltage of the field-effect transistor M2, is made dependent on the temperature. Further, the document discloses that since a temperature coefficient TCR of the output voltage VPN changes depending on a ratio of channel lengths L, by adjusting the ratio of channel lengths L, a desired temperature coefficient TCR can be obtained.    Patent Document 1:
Japanese Patent Kokai Publication No. JP-H09-133587 A, which corresponds to U.S. Pat. No. 5,914,629.    Patent Document 2:
Japanese Patent Kokai Publication No. JP2006-242894 A, which corresponds to US Patent Application Publication No. US2006/0197581A1.